Production of castings with coatings composed of high-chromium alloys



Patented 21,1933

UNITED STATES:

PATENT OFFICE f STANLEY NORWOOD, OF FLUSHING, NEW YORK, ASSIGNOR TO ELECTBO METALLUR- GICAL COMPANY, A CORPORATION OF WEST VIRGINIA mnuc'rron' or casrnms wrrri coa'rmos comrosnn or mon-cmioiunmr annoys Io Drawing.

The invention relates to the production of castings consisting of inner portions or base metal of iron or'steel and high-chromium alloy coatings which areresistant to abrasion and corrosion. The alloy coatings may contain about 12% or more of chromium but they commonly contain about 20% to 40% of chromium. The castings are made by pouring iron or steel into a mold which is covered with ferrochromium powder on the part or parts which correspond to the part or parts of the casting to be coated. The invention relates especially to the production of such castings or portions of castings in which the base metal is small in cross-section or volume. p

Hereto fore castings with high-chromium alloy surfaces have been made by pouring ferrous metal into molds which were lined with a powdered high-carbon ferrochromium. The

ferrochromium used for this purpose contained about 4% to 6% carbon, 0.5% to 2.0% silicon, and about 65% to 70% chromium. With this ferrochromium, suflicientalloying was obtained in casting large cross-sections and surfaces of small curvature to produce alloy coatings with proper thickness to give protection from oxidation or chemical ac tion. The coating'could not be chipped or scaled off and it would not separate from the core of cast metal when the body was bent orbnoken; When the castings had an edge or surface portion which was angular or had a great curvature, and@onsequently had a comparatively small crfiss section of base metal.

' associated with the portion, the alloying was incomplete; and continuous alloy, coatings ithisufiicient thickness to give the desired properties could not be formed.

40 The principal object of the invention is to provide means of producing smoothness in 'th'ealloy coatings and flowing of the alloy into an I lar corners of the molds.

Anot or object of the invention is to pro-' vide means of producing completely alloyed continuous coatings on portionsaof castings which have a great curvature.

Another ob'ect of the invent on 1s to provide means 0 producing complete alloying 60 on castings in which the core metal consists Application filed March 10, 1931. Serial No. 521,609.

der which passed through a number 20 sieve and was retained on a number sieve .was mixed with sodium silicate solution to make it adherent to the mold, and the walls of a mold were coated with a layer of the composition about one-sixteenth of an inch thick. The mold was adapted to produce a casting about two inches thick by four inches wide by eight inches long with rectangular faces. Thus the coatings along the sharp edges of the mold and around the solidfangles at the corners of the mold were subjected directly to theinfiuence of only a small volume or pencil of molten base metal when the base metal was poured. Carbon steel containing about 0.5% carbon was heatedto casting temperature and cast into the mold. Upon cooling, it was found that all'the corners and edges of the mold were completely filled and the base metal was completely covered with a uniform adherent coating of high-chromium alloy.

It has been found that the desired results can be obtained by the presenceof three to seven percent of silicon in the ferrochromium alloy powders used for lining the mold. The ferrochromium ma be varied from about 60% to 96% chromium, the remainder being iron withabout 3% to 7% silicon and about 1% to 6% carbon. Excellent results are obtained when about 4% to 6% carbon is present. The silicon may be present as an alloy constituent of the ferrochromium alloy, or ferrosilicon powder may be mixed with ferrochromium powder to give amixture of coating powder which 0 ntains the requisite proportion of chromium, carbon and silicon. The use of mixed ferrosilicon and ferrochromium powder has been found advantageous with base metals which can be'cast at lower temperatures than the temperatures cast iron.- The combination of powders has been found to .aid in fusing gether and alloying the base metal and the constituents the high chromium powder to produce high chromlum coatings, completealloying and perfect adhesion of the alloy coating to the chromium-containing alloy surface on'a ferrous alloy base metal cast in the mold, which comprises a metal powder containing ferrochromium carrying about 1% to 6% carbon andabout 60% to 95% chromium, and suflicient ferrosilicon to bring the silicon content of'the powder to about 3% to 7%.

In testimony whereof, I afiix my si ature. STANLEY M. NORW OD.

ase metal. The coarsest and finest particles of powder are'excluded but it is not essential 1 that all of the particles shall be of the same size.- Various mixtures which range in size from partlcles which W11]. be, retamed on [sieves about numbers 50 to 80 and will 'pass be used. Intermediate sizes may be used,'for Example powder which will pass through a I include through fsieves 'about numbers 16 .to 30 may number 30 sieve and; will be number 60 sieve.

'It is to be understood that alloy steels and hem may be used for the base metal as well retained on a 1 as carbon steel, that variations in the thick? ness of the coatings of powder and binder {and in the grading of the sizes of the particles may bemade to vary the thickness and character of the alloy coatings, and that the content of chromium and iron may be varied within wide lii'nits without departing from v the inventionf The term, mold as used in the specification" and claims refers to the matrix which is usedto f've shape to the casting and may lie core as well as the parts of the Y mold which constitute the receptacle. The

sieve numbers in the specification and claims refer tothe U. S. standard sieve numbers adopted by the American Society for Testing Materials.

I claim 2-- 1. A coating for molds adapted to form a chromium-containing allo surface on a ferrous alloy base metal cast in the mold, which comprises a fer'rochromium powder containing about 1% to 6% carbon and about 3% to 7% silicon. a

2. A coating for molds adapted to form a chromium-containing alloy surface on a' ferrous alloy base metal cast in the mold, which comprises a chromium alloy owder containing about 60.0% to 96.0% c omium, about 1% to 6% carbon and about 3% to 7% silicon. 3. A coating formolds adapted to form a chromium-containing alloy surface on a fer-- rous alloy base metal east in the mold, which comprises a layer of metal powder about one thirty-second to one-eighth of an inchin thickness, said powder containing about to 96% chromium, about 1% to 6% carbon, and about 3% to 7% silicon.

4. A coating for-molds adapted to form a 

